Treated graphene nanoplatelets for inflatable structure barrier layers

ABSTRACT

An air-impermeable fabric is disclosed. The air-impermeable fabric has a fabric substrate, which may also be referred to as a base fabric. Disposed over the fabric substrate is a barrier layer comprising a polymer binder and at least 20 weight percent graphene nanoplatelets, based on the total weight of the barrier layer. A barrier underlayer, which may or may not also include graphene nanoplatelets, is disposed between the fabric substrate and the barrier layer. A barrier overlayer, which may or may not also include graphene nanoplatelets, is disposed on the opposite side of the barrier layer from the barrier underlayer

This is a continuation-in-part of U.S. patent application Ser. No.13/490,083, filed Jun. 6, 2012, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to air-impermeable fabrics, and moreparticularly, to fabrics used for emergency evacuation equipment foraircraft evacuation such as evacuation slides and life rafts, as well asother inflatable structures such as for cushions and other emergency andnon-emergency applications.

The requirement for reliably evacuating airline passengers in the eventof an emergency is well known. Emergencies at take-off and landing oftendemand swift removal of the passengers from the aircraft because of thepotential for injuries from fire, explosion, or sinking in water. Aconventional method of quickly evacuating a large number of passengersfrom an aircraft is to provide multiple emergency exits, each of whichis equipped with an inflatable evacuation slide, which often doubles asa life raft in the event of a water evacuation. These evacuation slidesare most commonly constructed of an air-impervious coated fabricmaterial that is formed into a plurality of tubular members. Wheninflated, these tubular members form a self-supporting structure with aslide surface capable of supporting the passengers being evacuated. Inaddition to being air-impervious, the fabric material from which thetubular members are constructed must meet FAA specification requirementsof TSO-C69c for resistance to radiant heat, flammability, contaminants,fungus and other requirements.

Although evacuation slides permit passengers to quickly and safelydescend from the level of the aircraft exit door to the ground, therequirement that each aircraft exit door be equipped with an inflatableevacuation slide means that substantial payload capacity must be devotedto account for the weight of multiple evacuation slides. Accordingly,there has long existed the desire in the industry to make the inflatableevacuation slides as light as possible. A significant portion of theweight of an emergency evacuation slide is the weight of the slidefabric itself. Accordingly, various attempts have been made to reducethe weight of the slide fabric. One accepted method has been to reducethe physical size of the structural members of the slide by increasingthe inflation pressure. Increased inflation pressure, however, causesgreater stress on the slide fabric and, therefore, the benefit of thereduced physical size is at least partially cancelled out by the need touse a heavier gauge of slide fabric in order to withstand higherinflation pressures. Current state of the art slide fabric consists of a72×72 yarns per inch nylon cloth made of ultra-high-tenacity nylonfibers. This 72×72 fabric by itself has a grab tensile strength ofapproximately 380 lbs in the warp direction and 320 lbs in the filldirection (as used herein grab tensile strength refers to the strengthmeasured by grabbing a sample of fabric, typically 4 inches wide,between a set of one inch wide jaws and pulling to failure.) The fabricis typically coated with multiple layers of an elastomeric polymer torender it impermeable to air as well as a radiant-heat-resistantcoating. This results in a strong, but heavy fabric, having a grabtensile strength of approximately 390 lbs. in the warp direction and inthe fill direction, but with an areal weight that can exceed 7.0 oz/yd².As can be determined from the foregoing, these coatings do notcontribute significantly to the strength of the fabric.

Graphene nanoplatelets have been incorporated into air retention (AR)coatings for inflatable fabric structures at least in part to providedesired levels of impermeability to air at reduced weights compared toconventional AR coatings, see, e.g., published US patent application US2012/0315407 A1. The shape of the graphene nanoplatelets and their lowpermeability to gas molecules are believed to enhance the airimpermeability of AR coatings by creating a tortious path through the ARlayer for gas molecules as they attempt to diffuse through the ARcoating. However, it has now been discovered that crosslinked ARcoatings containing graphene nanoplatelets can fail flammabilityperformance requirements even when state-of-the-art flame retardantadditive packages are included in the coating composition.

Although the above-described fabrics for inflatable structures haveachieved widespread use in the aviation industry, the disparaterequirements for strength, weight, and flame resistance, as well asother requirements, have resulted in a continuing need in the art fornew fabrics.

BRIEF DESCRIPTION OF THE INVENTION

As described in further detail below, the invention provides a newair-impermeable fabric. The air-impermeable fabric has a fabricsubstrate, which may also be referred to as a base fabric. Disposed overthe fabric substrate is a barrier layer comprising a polymer binder andgraphene nanoplatelets. The graphene nanoplatelets have been pre-treatedby contacting with a liquid organophosphorus flame retardant beforeincorporating them into a coating composition.

In other aspects of the invention, a method of making an air-impermeablefabric is provided. According to the method, graphene nanoplatelets arefirst pre-treated by contacting with a liquid organophosphorus flameretardant to form treated graphene nanoplatelets. The treated graphenenanoplatelets are dispersed in a coating composition comprising apolymer resin. The coating composition is then coated over a fabricsubstrate, after which it can be dried or cured.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an air-impermeable fabric asdescribed herein;

FIG. 2 is a side view of an aircraft evacuation slide as describedherein; and

FIG. 3 is a bottom view of an aircraft evacuation slide as describedherein.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the invention is directed to an air-impermeablefabric. It should be noted that, as used herein, the term “impermeable”does not refer to absolute or permanent impermeability, but rather to adegree of permeability sufficiently low to meet the functionalrequirements needed for any particular inflatable application. Thefabric substrate, or base fabric, can be formed from any type of fiberpossessing desired physical properties and processability. Nylon fibersare often used, at least in part due to the strength and strength toweight ratio possessed by nylon fabrics. Various nylons, such asnylon-6, 6 or nylon-6, can be used, as well as other known nylonpolymers. Other polymer fibers can also be used, such as polyester,other aromatic and/or aliphatic polyamides, liquid crystal polymers,etc. Natural fibers such as silk can also be used. Fiber diameters canbe selected to achieve desired properties such as fiber spacings inwoven fabric. Yarn counts can range from 30×30 yarns per inch to 90×90yarns per inch, or higher, and more particularly from 40×40 yarns perinch to 75×75 yarns per inch. The yarn count geometry can also beasymmetric (i.e. 40×60 yarns per inch) if needed.

The fiber strength of the base cloth can also be increased byincorporating nanoreinforcements into the polymeric matrix of the fiberitself. The nanoreinforcements can be carbon nanotubes, carbonnanofibers, grapheme nanoplatelets, polymeric nanofibers, metallicnanotubes or nanofibers, metal oxide nanotubes, metal oxide nanofibers,metal oxide nanoparticles or metal oxide nanoplatelets or a combinationthereof. The nanoreinforcements can be incorporated into the polymermatrix of the fiber during synthesis of the fiber matrix or processingof the matrix into fibers. For example, the nanoreinforcements can becombined with the neat polymer matrix prior to thermal processing intofibers. The nanoreinforcements can also be incorporated into themonomeric precursors used to synthesize the polymeric composition of thecloth fiber.

Graphene nanoplatelets are commercially available from sources such asXG Sciences, and can be prepared by mechanical and/or thermalexfoliation of graphite. Graphene nanoplatelets can be prepared invarious sizes, and those used in the barrier layer described herein canhave a thickness ranging from 2 nm to 50 nm, more particularly from 5 nmto 15 nm. The graphene nanoplatelets can have diameters ranging from 0.5μm to 50 μm, more particularly from 5 μm to 25 μm (note that diameter onthe hexagonal-shaped nanoplatelets is defined as the distance betweenopposite corners of the hexagon). The barrier layer can comprise variousamounts of graphene nanoplatelets. In some exemplary embodiments, thebarrier layer comprises 0.5 wt. % to 90 wt. % graphene nanoplatelets,based on the total weight of the barrier layer (i.e., the curedcoating). In some exemplary embodiments, the barrier layer comprises 0.5wt. % to 5 wt. %, more particularly 1 wt. % to 4 wt. %, and even moreparticularly 1 wt. % to 3 wt. %, of graphene nanoplatelets, thepercentages based on the total weight of the barrier layer (i.e., thecured coating). In some exemplary embodiments, the barrier layercomprises 20 wt. % to 90 wt. %, more particularly 20 wt. % to 60 wt. %,more particularly 25 wt. % to 45 wt. %, and even more particularly 25wt. % to 35 wt. % of graphene nanoplatelets, the percentages based onthe total weight of the barrier layer (i.e., the cured coating).

As mentioned above, the graphene nanoplatelets are pre-treated bycontacting with a liquid organophosphorus flame retardant.Organophosphorus flame retardants are commercially available, andinclude for example, organophosphates such as such astris(2-propylphenyl)phosphate, triphenyl phosphate (TPP), resorcinolbis(diphenylphosphate) (RDP), bisphenol A diphenyl phosphate (BADP), andtricresyl phosphate (TCP); phosphonates such as dimethylmethylphosphonate (DMMP); and phosphinates such as aluminum diethylphosphinate. Organic compounds can also be used that contain bothphosphorus and a halogen. Such compounds includetris(2,3-dibromopropyl)phosphate (brominated tris) and chlorinatedorganophosphates such as tris(1,3-dichloro-2-propyl)phosphate(chlorinated tris or TDCPP) andtetrakis(2-chlorethyl)dichloroisopentyldiphosphate. The duration ofpre-treatment contacting (i.e., contacting time) of the graphenenanoplatelets can vary, and in some embodiments is at least 10 minutes,more particularly at least 120 minutes, and even more particularly atleast 24 hours accompanied by ultrasonic agitation. An upper durationlimit is not specified, as it is limited only by process efficiencyconsiderations. Although it is contemplated that pure liquidorganophosphorus flame retardant (including substantially pure, withinthe limits of manufacturing and analytical capabilities) is used topre-treat the graphene nanoplatelets, other materials can be present aswell, including but not limited to other flame retardants, solvents,etc. In some embodiments, the pre-treatment liquid comprises at least0.5 wt. % liquid organophosphorus flame retardant, more particularly atleast 1.5 wt. % liquid organophosphorus flame retardant, and even moreparticularly at least 3.0 wt. % liquid organophosphorus flame retardant.

The resin used for the barrier layer as well as other layers on thefabric can be chosen from various polymers. Polyurethane polymers andpolyurethane-containing copolymers are often used, at least in part duetheir elasticity and durability. Well-known polyurethane chemistryallows for various aromatic and/or aliphatic polyisocyanates and polyolsto be reacted together to provide desired coating characteristics, andsuch coating resins are readily commercially available. Other polymerscan be readily copolymerized with polyurethanes, often through inclusionof hydroxy-terminated prepolymers (e.g., OH-terminated polyester orOH-terminated polycarbonate) in the polyisocyanate/polyol reaction mix.In some embodiments, a polymer resin other than polyurethane is used,e.g., polyester. Resins can include functional groups, such as hydroxyl,carboxyl, amino, other resin functional groups known in the art. Blendsof one or more of polymer resins such as those described above can alsobe included in a coating composition.

The coating composition can also contain one or more crosslinkers.Crosslinkers are selected to have reactivity with the functional groupson the polymer resin, and can include, for example, polyfunctionalalcohols (e.g., trimethylolpropane) polyfunctional alcohol reactivecompounds (e.g., melamine), polyfunctional isocyanates (e.g.,trifunctional isocyanurate compounds formed by diisocyanates such asmethylenediphenyl diisocyanate (MDI) or isophorone diisocyanate (IPDI)),polyfunctional acids (e.g., tricarballylic acid), polycarbodiimides orpolyazidines. The amount of crosslinker can be adjusted by those skilledin the art to achieve desired properties. In addition to acceleratingcure, added crosslinker tends to increase coating hardness and decreaseelasticity. The coating composition may also contain one or morevolatile liquids, including water and/or various polar or non-polarorganic solvents. Such volatile liquids are vaporized before or duringcure and do not form part of the cured or finished coating. Reactivediluents (i.e., organic compounds that function as a solvent duringapplication of a polymer resin-containing coating composition, but havefunctional groups that react with the polymer during cure so that theyform part of the cured coating.

The treated graphene nanoplatelets have been demonstrated to provideenhanced flame resistance in crosslinked AR coatings. The inventiondescribed herein is not bound by any particular theory or mechanism;however, it is believed that in some exemplary embodiments, flammableside products such as alcohols, aldehydes and/or ethers released duringcure are trapped in the AR layer by the nanoplatelets (e.g., blockedfrom diffusing out and/or absorbed by the graphene nanoplatelets). Insuch embodiments, pre-treatment of the graphene nanoplatelets couldinterfere with combustion of such side products and/or interfere withabsorption of such side products by the graphene nanoplatelets. Suchside products can be formed by the crosslinking reaction betweenfunctional groups on the polymer resin and alkoxymethylol-substitutedamino groups on the crosslinker such as found on melamine derivativeslike hexamethoxymethylol melamine (HMMM), hexabutoxymethylol melamine,etc. Of course, such melamine derivatives need not be hexa-substitutedwith such groups to produce such side products. Accordingly, in someexemplary embodiments, the coating composition comprises analkoxymethylol-substituted melamine derivative crosslinking agent. Infurther exemplary embodiments, the coating composition comprises ahydroxy-functional polymer resin such as a hydroxy-functionalpolyurethane as well as additional functionalities that may permitcrosslinking via other crosslinker chemistries. Curing for suchcrosslinkable coating compositions can be effected at an elevatedtemperature to promote the crosslinking reaction. In some embodiments,curing takes place at temperatures of 120° C. to 160° C., and moreparticularly 140° C. to 160° C., for periods of from 1 to 15 minutes,more particularly from 2 to 10 minutes. Cure temperatures and times canalso be reduced by adding a para-toluene sulfonic acid-based catalyst.

The coating compositions applied to form any of the coatings on thefabric described herein can include various additives ordinarilyincorporated into coating compositions Such additives can be mixed at asuitable time during the mixing of the components for forming thecomposition, and include fillers, reinforcing agents, antioxidants, heatstabilizers, biocides, plasticizers, lubricants, antistatic agents,colorants, surface effect additives, radiation light stabilizers(including ultraviolet (UV) light stabilizers), stabilizers, and flameretardants. Such additives can be used in various amounts, generallyfrom 0.01 to 5 wt. %, based on the total weight of the coatingcomposition

In addition to the organophosphorus flame retardant used forpre-treatment, the barrier layer can include one or more other flameretardants, including but not limited to the same flame retardant usedfor pre-treatment. Exemplary flame retardants includephosphorous-containing compounds such as organophosphates (e.g.,tris(2-butoxy)ethylphosphate (TBEP), tris(2-propylphenyl)phosphate,organophosphonates (e.g., dimethylphosphonate), organophosphinates(e.g., aluminum diethylphosphinate), inorganic polyphosphates (e.g.,ammonium polyphosphate)), organohalogen compounds (e.g.,decabromodiphenyl ethane, decabromodiphenyl ether, and variousbrominated polymers or monomers), compounds with both halogen andphosphorous-containing groups (e.g., tris(2,3-dibromopropyl)phosphate),as well as other known flame retardants. Brominated flame retardants areoften used in combination with a synergist such as oxides of antimony(e.g., SbO₃, Sb₂O₅) and other forms of antimony such as sodiumantimonite. The amount of flame retardant can vary widely depending onthe particular flame retardant or combination of flame retardants, withexemplary amounts ranging from 5 wt. % to 50 wt. %, more particularlyfrom 10 wt. % to 25 wt. %.

Other coating layers can be present in addition the above-describedbarrier layer. In some embodiments, a heat-resistant (HR) layer is alsopresent, often on the side of the fabric that will be the outside of theinflatable structure. HR layers can comprise a high temperature polymerresin binder and aluminum pigment. HR layers can contain at least 10 wt.% aluminum pigment. An exemplary formulation contains between 0.1 wt. %and 10 wt. % microspheres. A further exemplary formulation containsbetween 1 wt. % and 5 wt. % microspheres. In addition to radiant heatreflecting properties provided by the aluminum pigment, a heat-resistantlayer can also include heat-absorbing additives such as ceramicmicrospheres. HR layers can contain at least 0.11 wt. % microspheres. Anexemplary formulation contains between 0.11 wt. % and 6.2 wt. %microspheres. A further exemplary formulation contains between 1.1 wt. %and 2.1 wt. % microspheres. All weight percentages are based on thetotal weight of the layer. Tie coat layers can also be present. Tiecoats are utilized to provide greater adhesion to the substrate thanmight be provided by the various functional layers. For example, apolyurethane-polycarbonate copolymer resin can be used in a tie coatapplied directly to the fabric surface where its relatively low modulusof elasticity provides good conformation of the resin to the clothmorphology while the relatively higher modulus of elasticity of apolyurethane polymer resin used as binder for a barrier layer providesthe necessary strength and flexibility to maintain overall coatingintegrity and air impermeability when subjected to deformation andstress during inflation.

Turning now to the figures, FIG. 1 schematically depicts a cross-sectionview of an exemplary air-impermeable fabric 100 according to theinvention. As shown in FIG. 1, fabric substrate 110 has barrier layer120 disposed thereon. On the other side of fabric substrate 110 is aheat-resistant layer 130 such as an aluminized coating. The abovearrangement provides air retention (AR) layers on one side of the fabricthat can face the interior of an inflatable structure and aheat-resistant layer 130 on the other side of the fabric that would bethe exterior of an inflatable structure. This arrangement providesresistance to heat from external sources such as fire on the outside ofan inflatable structure while keeping the critical AR layers furtheraway from such external heat sources. Of course, other layerarrangements can be used as well. For example, the AR layers could bedisposed between the base fabric and an outermost heat-resistant layer.

Turning now to FIG. 2, an inflatable evacuation slide assembly 10 isdepicted incorporating features of the present invention. Evacuationslide assembly 10 generally comprises a head end 12, and a foot end 14terminating at toe end 16. Head end 12 is configured to coupleevacuation slide assembly 12 to an exit door 18 of an aircraft 20 whilefoot end 14 is in contact with the ground 22 such that the slideassembly 10 provides a sloping surface to permit the rapid egress ofpassengers from aircraft 20.

With reference to FIGS. 2 and 3, the main body of evacuation slideassembly 10 comprises a plurality of inflatable flexible membersincluding side rail tubes 24, 26 which extend from head end trussassembly 28 to the ground 22. A slide surface 30 comprising a fabricmembrane is stretched between side rail tubes 24 and 26 to provide asliding surface for the disembarking passengers. A right hand rail 32and a left hand rail (not shown) are positioned atop side rail tubes 24and 26, respectively, to provide a hand hold for passengers descendingevacuation slide assembly 10. Head end truss assembly 28 comprises aplurality of strut tubes 36, 38, upright tubes 40, 42 and a transversetube 44 adapted to hold head end 12 of evacuation slide assembly 10against the fuselage of aircraft 20 in an orientation to permit escapeslide assembly 10 to unfurl in a controlled manner as it extends towardthe ground.

The spaced apart configuration of side rail tubes 24 and 26 ismaintained by a head end transverse tube 46, a toe end transverse tube48, a foot end transverse truss 52 and medial transverse truss 54. Thebending strength of escape slide assembly 10 is enhanced by means of oneor more tension straps 50 stretched from toe end 16 over foot endtransverse truss 52, medial transverse truss 54 and attached proximalhead end 12 of evacuation slide assembly 10. As described, evacuationslide assembly 10 provides a lightweight structure that consumes aminimum amount of inflation gas while providing the necessary structuralrigidity to permit passengers to safely evacuate an aircraft underemergency conditions.

The entire inflatable evacuation slide assembly 10 can be fabricatedfrom an air impervious material described more fully hereinafter. Thevarious parts of the inflatable evacuation slide assembly 10 may bejoined together with a suitable adhesive whereby the structure will forma unitary composite structure capable of maintaining its shape duringoperation. The entire structure of the inflatable evacuation slideassembly 10 can be formed such that all of the chambers comprising thestructure are interconnected pneumatically, such that a singlepressurized gas source, such as compressed carbon dioxide, nitrogen,argon, a pyrotechnic gas generator or combination thereof may beutilized for its deployment.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLES

Test samples were prepared by coating a 60×60 yarns per inchultra-high-tenacity nylon fabric with a coating composition comprising apolycarbonate polyurethane resin (Stahl Permuthane SU21-591), a flameretardant additive package comprising decabromodiphenylethane (DBDPE)and an SbO₃ synergist. A crosslinker (hexamethoxymethylol melamine(HMMM), Stahl XR91-110) was included in the coating composition on someof the samples, as indicated in Table 1. Graphene nanoplatelets (XGSciences, Grades M5, M15 and M25, with mean particle diameters ofapproximately 5, 15 and 25 microns) were also included in the coatingcomposition for some of the samples, with the GNP are either untreatedor treated by mixing for a minimum of 60 minutes with a 1-20 wt. %solution of tri(2-propylphenyl)phosphate in toluene, dimethylformamide,2-propanol or other solvent compatible with the polyurethane resin.Individual or a mixture of the solvents can be utilized as shown inTable 1. The samples were tested for flame resistance using a 12 secondvertical flammability test according to ASTM D-6413 “Standard TestMethod for Flame Resistance of Textiles, and for adhesion according toan adapted version of ASTM D4651. The results are shown in Table 1.

TABLE 1 GNPs 12 sec. Vertical Adhesion HMMM Not OP(Or): FlammabilitySpecification Sample crosslinker treated Treated test (SP-733) A X X —Fail Pass B — X — Pass Fail D X — — Pass Pass E X — X Pass Pass

As shown in Table 1, the control sample D without graphene nanoplateletspassed both the flammability test and the adhesion test. However, whengraphene nanoplatelets were introduced for payload weight and airretention purposes, the sample (B) failed the adhesion test unlesscrosslinker with 160° C. cure was added. However, the crosslinked sampleA failed the flammability test. The graphene nanoplatelet-containingsample with the crosslinker and pre-treated graphene nanoplateletspassed both the flammability and adhesion tests. The beneficial resultsprovided by treated graphene nanoplatelets are of course not limited tocrosslinked coatings, and may provide flammability benefits innon-crosslinked coatings under different testing protocols than thoseused for this particular application.

Additional test samples were prepared by coating a 60×60 yarns per inchultra-high-tenacity nylon fabric on one side with first and second airretentive layers (Layer1 and Layer2) as shown in Table 2, and on theother side with an aluminum pigment-containing radiant heat resistantcoating. Individual layers were applied to yield a final areal weightabout 0.20-0.60 oz./yd² per layer. Samples F, G, and H differed in thegrade, version, or source of organophosphate and/or Sb synergist.Samples J and K also differed in the grade, type, or source oforganophosphate and/or Sb synergist. The air retentive coatings forsamples F through L were formulated using two individual premixes,premix A containing the graphene nanoplatelets and theorganophosphate/solvent blend and premix B incorporating all remainingcomponents. After the premixes were mixed sufficiently, premix Aincorporating the graphene nanoplatelets is added to premix B. Forsample M, graphene nanoplatelets were pre-treated for 120 minutes in thespecified solution of toluene solvent and phosphorus-based flameretardant, following which the mixture of GNP's with toluene and flameretardant (Premix A) were mixed with the other components of the coatingcomposition (Premix B).

TABLE 2 F G H I Sample Layer1 Layer2 Layer1 Layer2 Layer1 Layer2 Layer1Layer2 Toluene — — — — — — — — Triaryl phosphates — — — — — — — —isopropylated, CAS # 68937-41-7 Graphene — — — — — — — — nanoplateletsM-25, XG Sciences Toluene 50.00  50.00  50.00  50.00  50.00  50.00 50.00  50.00  Dimethylformamide 10.00  10.00  10.00  10.00  10.00 10.00  10.00  10.00  Graphene 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00nanoplatelets GNP-MSTC, Goodrich Corp. Graphene — — — — — — — —nanoplatelets M-25, XG Sciences N,N-dioctyloctan- 0.50 0.50 0.50 0.500.50 0.50 0.50 0.50 1-amine Glycidoxypropyl — — — — — — — —trimethoxysilane CAS # 2530-83-8 Gamma-aminopropyl — 1.00 — 1.00 — 1.00— 1.00 triethoxysilane CAS# 919-30-2 Irgaguard F3000 0.25 0.25 0.25 0.250.25 0.25 0.25 0.25 fungicide Ethane-1,2-bis 3.00 3.00 3.00 3.00 3.003.00 — — (pentabromo- phenyl) SbO₃ — — — — — — — — Tris(2-butoxy) 2.502.50 2.50 2.50 2.50 2.50 2.50 2.50 ethylphosphate Stahl Permuthane —200    — 200    — 200    — 200    SU21-591 resin Bayer Impranil 160    —160    — 160    — 160    — ELH-1/A Hexamethoxy — — — — — — — —methylolmelamine, Stahl XR91-110 J K L M Sample Layer1 Layer2 Layer1Layer2 — Layer1 Layer2 Toluene — — — — — 25.00 25.00 Triaryl phosphates— — — — — 3.00 3.00 isopropylated, CAS # 68937-41-7 Graphene — — — — —1.50 1.50 nanoplatelets M-25, XG Sciences Toluene — — — — 20.00 — —Dimethylformamide — — — — — — — Graphene — — — — — — — nanoplateletsGNP-MSTC, Goodrich Corp. Graphene 2.50 2.50 2.50 2.50 2.0  — —nanoplatelets M-25, XG Sciences N,N-dioctyloctan- — — — — — — — 1-amineGlycidoxypropyl — — — — 1.00 — — trimethoxysilane CAS # 2530-83-8Gamma-aminopropyl — — — — — — — triethoxysilane CAS# 919-30-2 IrgaguardF3000 0.25 0.25 0.25 0.25 0.25 0.25 0.25 fungicide Ethane-1,2-bis 20.63 20.63  20.63  20.63  20.63  20.00  20.00  (pentabromo- phenyl) SbO₃ 7.507.50 7.50 7.50 7.50 7.00 7.00 Tris(2-butoxy) 9.38 9.38 9.38 9.38 9.38 —— ethylphosphate Stahl Permuthane 200    200    200    200    200   200    200    SU21-591 resin Bayer Impranil — — — — — — — ELH-1/AHexamethoxy — — — — 10.0  3.0  6.0  methylolmelamine, Stahl XR91-110

The samples were subjected to flammability testing according to anadapted version of ASTM 6413. The results are shown in Table 3.

TABLE 3 Time to Burn length Drip end time Flammability Sample extinguish(sec.) (in.) (sec.) Pass/Fail I 42.0 12.0 0 Fail F 29.7 12.0 0 Fail G11.3 6.5 0 Pass H 10.7 6.3 0 Pass J 1.0 5.0 0 Pass K 0.0 4.3 0 Pass L40.0 12.0 0 Fail M 0.0 4.3 0 Pass

As shown in Table 3, the addition of SbO₃ synergist and the accompanyinghigher amounts of bromine-based flame retardant (samples J and K)provided a significant benefit in time to extinguish and burn length.However, these samples did not include a crosslinking agent, which isoften needed in order to meet coating adhesion or other physicalproperty requirements. Sample L included such a crosslinking agent, butexhibited significantly worse results in both time to extinguish andburn length. Sample M, which utilized GNPs pre-treated inphosphorous-base flame retardant provided significant benefits in bothtime to extinguish and burn length even when a crosslinking agent ispresent.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise, and “or” means“and/or”. The modifier “about” used in connection with a quantity isinclusive of the stated value and has the meaning dictated by thecontext (e.g., includes the degree of error associated with measurementof the particular quantity). The terms “front”, “back”, “bottom”, and/or“top” are used herein, unless otherwise noted, merely for convenience ofdescription, and are not limited to any one position or spatialorientation. The endpoints of all ranges directed to the same componentor property are inclusive and independently combinable (e.g., ranges of“less than or equal to 25 wt %, or 5 wt % to 20 wt %,” is inclusive ofthe endpoints and all intermediate values of the ranges of “5 wt % to 25wt %,” etc.). The suffix “(s)” is intended to include both the singularand the plural of the term that it modifies, thereby including at leastone of that term (e.g., “the colorant(s)” includes a single colorant ortwo or more colorants, i.e., at least one colorant). “Optional” or“optionally” means that the subsequently described event or circumstancecan or can not occur, and that the description includes instances wherethe event occurs and instances where it does not. Unless definedotherwise, technical and scientific terms used herein have the samemeaning as is commonly understood by one of skill in the art to whichthis invention belongs.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. An air-impermeable fabric, comprising a fabric substrate; and abarrier layer comprising graphene nanoplatelets that have beenpre-treated by contact with a liquid organophosphorus flame retardantcompound, and a polymer resin.
 2. The air-impermeable fabric of claim 1,wherein the barrier layer comprises from 0.5 wt. % to 90 wt. % ofgraphene nanoplatelets, based on the total weight of the barrier layer.3. The air-impermeable fabric of claim 2, wherein the barrier layercomprises from 0.5 wt. % to 5 wt. % of graphene nanoplatelets, based onthe total weight of the barrier layer.
 4. The air-impermeable fabric ofclaim 1, wherein the barrier layer comprises from 20 wt. % to 90 wt. %of the graphene nanoplatelets, based on the total weight of the barrierlayer.
 5. The air-impermeable fabric of claim 1, wherein the barrierlayer comprises from 25 wt. % to 45 wt. % of the graphene nanoplatelets,based on the total weight of the barrier layer.
 6. The air-impermeablefabric of claim 1, wherein the liquid organophosphorus flame retardantis an organophosphate.
 7. The air-impermeable fabric of claim 1, whereinthe barrier layer is a cured coating produced by a coating compositioncomprising the pre-treated graphene nanoplatelets, the polymer resin,and a crosslinking agent.
 8. The air-impermeable fabric of claim 7,wherein polymer resin comprises hydroxy functional groups and thecrosslinking agent is an alkoxymethylol-substituted melamine derivative.9. The air-impermeable fabric of claim 8, wherein polymer resincomprises a hydroxy-functional polyurethane.
 10. A method of making anair-impermeable fabric, comprising contacting graphene nanoplateletswith a liquid organophosphorus flame retardant to form pre-treatedgraphene nanoplatelets; dispersing the pre-treated graphenenanoplatelets in a coating composition comprising a polymer resin; andcoating the coating composition over a fabric substrate.
 11. The methodof claim 10, wherein the barrier layer comprises from 0.5 wt. % to 90wt. % of graphene nanoplatelets, based on the total weight of thebarrier layer.
 12. The method of claim 11, wherein the barrier layercomprises from 0.5 wt. % to 5 wt. % of graphene nanoplatelets, based onthe total weight of the barrier layer.
 13. The method of claim 10,wherein the barrier layer comprises from 20 wt. % to 90 wt. % of thegraphene nanoplatelets, based on the total weight of the barrier layer.14. The method of claim 10, wherein the barrier layer comprises from 25wt. % to 45 wt. % of the graphene nanoplatelets, based on the totalweight of the barrier layer.
 15. The method of claim 10, wherein theliquid organophosphorus flame retardant is an organophosphate.
 16. Themethod of claim 10, wherein the coating composition further comprises acrosslinking agent.
 17. The method of claim 16, wherein polymer resincomprises hydroxy functional groups and the crosslinking agent is analkoxymethylol-substituted melamine derivative.
 18. The method of claim17, wherein polymer resin comprises a hydroxy-functional polyurethane.19. An inflatable structure comprising the air-impermeable fabric ofclaim
 1. 20. The inflatable structure of claim 19 that is an aircraftevacuation slide.